Receiving system



Sept. 9, 1930. I A. A. KENT 1,775,399

RECEIVING sYsTBI Filed Jan. 27, 1928 2 Shuts-Shoot 1 Sept. 9, 1930. A, NT 1,775,399

VV VVVVVVVVVV El 928 v 2 Shuts-Shut 2 ll atentecl m'reo STATES PATENT OFFICE RECEIVING SYSTEM Application filed January 27, 1928. Serial No. 249,785.

My invention relates to the control of magnitude of amplification or volume of reproduction of speech, music and other signals, in radio receivin systems, more particularly ip a those in whic the source of power for the anode circuits and for heating the cathodes of thermionic vacuum tubes is of the alternating current type.

In accordance with m invention a resist- ,w ance, which may be non-inductive or more or less inductive, is operatively related to the input system or circuit of a thermionic vacuum tube, of the audion type, comprised in a radio receiving system, and 'more particularly it to the input system or circuit of an amplifier tube, more especially a radio frequency amplifier tube, and preferably to the input sys tem or circuit of the first-stage radio frequency amplifier, and is variable by a co- 7 an acting control contact smoothly and gradually to change its shunting effect upon the input system or circuit with which it is operatively related to effect the desired volume control. The resistance variation is characteraliized by the fact that for equal increments of movement of the control contact there are effected smaller magnitudes of resistance change in the region corresponding to low volume than in the region corresponding to to higher volume, and to this end the resistance conductor is so wound or disposed upon a form or support that the spacing of the turns of the resistance conductor increases from the region of high to the region of low volac ance, and, more particularly, the resistance conductor comprises two or more sections in which the spacing of turns is greater in a section adjacent the region corresponding to low volume than in a section adjacent the refi gion corresponding to high volume.

More particularly the variable resistance of the character aforesaid is associated with the first-stage radio frequency amplifier tube, operating as a coupling tube between the antenna or other absorption structure and a cirvcuit or circuits tunable throughout a wave length range without effect thereon by the input system or circuit of the couplingtube whose inductance and capacity remain. subin stantially constant throughout the tuning range notwithstanding variation of the volume-controlling resistance; and where the cou ling tube intervenes between the antenna or a sorption structure and a plurality of cascaded tunable circuits the movable elements of their tuning devices may be mechanically coupled for operation in unison.

My invention resides in a system of volume control of the character hereinafter described and claimed.

For an understanding of my invention and for an illustration of some of the various forms it may take, reference is to be had to the accompanying drawings, in which:

Fig. lis a diagrammatic view of a receiving system embodying my invention.

Fig. 2 is an elevational view of. tuning condrlmsers whose rotors are mechanically cou- P e Fig. 3 is a side elevational view of a resistance unit." I

Fig. 4 is a cross-sectional view, partly in elevation, of the unit shown in Fig. 3.

Fig. 5 is a sectional view, partly in elevation, illustrative of the mounting of the resistance unit and its co-acting control contact. i

Fig. 6 is an end elevational View of the structure shown in Fig. 5.

Fig. 7 is a side elevational view of a modi-- fied form of resistance unit.

Fig. 8 is a graph illustrative of the characteristic of the volume control.

Referring to Fig. 1, the received electro-radiant energy is absorbed by the antenna A or any other e uivalent absoaption structure.

In the examp e illustrated is a thermiomc radio frequency amplifier tube utilized as a coupling tube in the first-stage of a cascade of radio frequency amplifying, detecting and audio frequency amplifying tubes. Its gr d 9 is connected to the antenna A whileits cathode or filament f is connected to earth or countercapacity E through the condensers k, 'k which exhibit low reactance at the radio frequencies involved. Connected between grid 9 and earthor couu-tercap'acity E is the radio frequency choke coil L which substantially completely prevents passage of radio frequency current therethrough, but serves as a by-pass for low or audio frequency disturbances to prevent any substantial effect thereof upon the grid g.

In the circuit of the anode or plate a of the tube V is the primary of a radio frequency transformer preferably having high step-up ratio and whose secondary is shunted by the variable tuning condenser C one of whose terminals is connected to earth E and the other through the stabilizing resistance 1', generally of several hundred ohms, to the grid 9 of the radio frequency amplifier tube V In the anode circuit of the latter is the primary of a second radio frequency step-up transformer T whose secondary is shunted by the variable tuning condenser C one of whose terminals is grounded at E and the other of which connects through a stabilizing resistance r with the grid 9 of the radio frequency amplifier tube V in whoseanode circuit is the primary of a step-up rad o frequency transformer T whose secondary 1s shunted by the variable tuning condenser C one of whose terminals is connected to E and the other connects through the small grid condenser /c to the grid g of the detector tube V having the equi-potential cathode 7 brought to incandescence by the heater h traversed by alternating current. Between the grid 9 and cathode f is connected the grid leak resistance r of high magnitude. Between the cathode f and the anode a is connected the condenser I0 and in the anode circuit is the primary of the audio frequency transformer T whose secondary is in the in put circuit of the audio frequency amplifier tube V whose anode circuit is coupled by the audio frequency transformer T" with the input circuit of the audio frequency amplifier tube V in whose anode circuit are connected the condenser 10 and the reproducing or signal translating instrument, such as a loud speaker S.

G represents generically any source of alternating current, such for example one delivering current at a frequency of 60 cycles per second. Through a lamp socket or other equivalent switching or connecting means 5 the primary of the transformer T is connected with the source G. The transformer T has several secondary windings of which 1 supplies so-called raw alternating current to the filaments of the tubes V, V V and V 2 supplies alternating currentto the heater 71. of the detector tube V; and 4 supplies alternating current to the filament of the power amplifying tube V. The secondary 5 delivers alternating current to the filament of the double-wave rectifying tube 6 whose anodes are connected to opposite ends of the secondary 7. W'ith these transformer secondaries are associated resistances, condensers, and choke coils, constituting an alternating current power unit for supplying current for heating the cathodes of the several tubes, and for supplying filtered rectified alternating current at various suitable voltages for the anode circuits of the tubes.

A system of the character above described is a typical tuned radio frequency amplifier receiving utilizing alternating current or socket power.

The input system of tht first tube V comprising the antenna and earth connections and the choke coil L, which latter may be omit-ted if suitable or desirable, is of substantially constant inductance and capacity with the result that there is no reactive effect, due to the intervention of the tube V, upon the first tuned comprising the condenser C. It is therefore practicable to mechanically couple the rotors of the several tuning condensers C, C and C for single dial tuning or uni-control. indicated in Fig. 2 in which the several condenser stators are indicated at 8, 9 and 10 and their cooperating rotors are indicated at 11, 12 and 13. On the shafts of the rotors are pulleys 14 coupled by the bands or belts 15 and 16 which may be of metallic ribbon. The rotors and stators of the tuning condensers are of such character that in their cooperation equal increments of angular adjustment of ments of capacity change.

The volume control resistance R is connected at its one terminal 17 with earth E or cathode f of the tube V. Movable along the resistance is the control contact K connected to the grid 9 of the tube V. By moving the contact K along the resistance R there is produced a variable shunting effect upon the input system or circuit of the tube V,

decreasing the potential of grid 9 as the contact K is moved towards the terminal 17. Accordingly the signal effect impressed upon the tube V is varied, with resultant control of the volume of the sounds emitted by the radio speaker S.

The conductor of the resistance R is preferably of high specific resistance, such as advance wire or the like. The spacing of the turns however is different at different positions along the resistance R from its upper end 18 to its terminal 17. In the example illustrated resistance R comprises three serially connected sections R R and R The turns of section R are closely spaced, those of R more widely spaced, and the spacing of the turns of the section R are still more widely spaced. The resistance R is more or less inductive when constructed as hereinafter described. In consequence not only the resistance of R in shunt to the input terminals of the tube V is varied by adjustment of the control contact K.

Such mechanical coupling is their rotors effect equal increbut also the inductance of the resistance R is wound in the form of a l rj esistancc and inductance insu at ng hat-M15119; Asihdicate'd the Seeeral sections R, R andR havetheir turns differently spaced, with the resiilt i that per 1;! le th on t e e tion R less in sectionR an dstill lessin section R For example "sectidn nyma be; t inches long, 120 'tur 1b) 1 rich; and section R, 1 in'chflong section B may be 1 inch'long,

turns per The conductor throughoutfthe sev- 1 eral sections may be Advanceorother suit L able; Wi e; about No. v 36 gauge When the laiiSt i 'ip lis 1/2 inch wide and about 1/16 inch;

1 thickthe entire non-inductive resistance of he t'hree sectionsis about 460ohmsfwith an ndi ctanceof about microhenrys of which [{microhenrys inthe section B.

1 51 111 11 1161 winding the resistance conductor f: in two or: more sections, "with the turns in f each sectionuniformly spaced, but differently .s 1 aced inthe different sections", the conductor be we lh ifi inei td inFig. with nuous and progr ss1ve1 ncrease 1n spacng Furthermore 3 and 7 the widthofr the form 19 l mayjtaper from one o member; It may be;wider at the 1 8 orfand preferably; it nay be narrower dmcent'the 117 than at the end 18. The resistance unit of Fig; 3 or 7 maybe contact K asfindicated' "which h wev'er there isillustrated the secsuitably mounted with gnatimwits control tioned resistance" unit of Fig 31' A' ircullar' housing for Q0, preferably of .nioldedyinsulating material such as ivhich latter lso eqnstittte's the terminal 17 with which Communicates a, connecting condvucto r 26, "I lherotatable operators'ltnob 27 ,is secured to the shaft 128 which has a bearing a "st/enema the metallic ,shaft 28 is the contactfarm 29 tvhose outer end constitutes the control contact" K which is 1 Carried by the top jfi ls 'm Y le lqnsfl thll edg e 'td 1 i unit, A- conducting "niemberBO niai'nt'ains electrical contactwith'theshaft28 and there if orecwith the contact has ics outer" e ndgsecured to the casingQO bythe nut 31 vvhich serves also as a bin "i conk v i i g l w l w 1 the resistance unifithe' co: act"jK"may pass ofi of the resistance" conductorandthereby 1 tt htiii uteri theeaip' platepfi the unit the eatestinsec er itihf; the" length range f rom about 200-to about, 600 40 turns is broughton to the' end 18 of the resistance adjacentthe ter'miriall'Z' than at the end ng post for the tthe end 18 of opeir the shunting-circuit including the re- {sistance unit; When soout of contact for a given amplitude of radio frequency energy *{abjsorbed by the antennawAthe potential of grid '9 of the tube V-is at maximum and is notto='anyappreciable extent reducedby the shunting chokeicoilL whose inductance may be'of the order oflGOO microhenrys fora receiving system tunable throughout a a "wave metersfi To reduce the volume the contact K unit "whereupon-there is immediately some shuntin'g effectwhich reducesthe effective potential of the gridof the tube V with a consequent reduction involume of reproductioir at the speaker S. As the contact K moves along the section R the resistance and inductancechange per unit length of movementofthe contact K is of the same magni -tude throughout traverse of the section R;

is less during traverse of the section R and is still less'in traversing section R. The

result is an increase of shunting efi'ect. and

therefore decrease of potential in thegril g of the tube V, as the contact K is moved from the end 18 toward theterminal 17 Inasmuchasthe turns arewmore widely spaced in sections RandR than in sectionR the inductance per turn of resistance conductor is greatestin section R less in section R and stilllessin seti0n R While the noninductive resistance per turn is practically the same throughoutzall the sections; At a given frequency of the received energy the inductive reactance in the'section R is smaller in comparison to the non-inductive resistance" thanin section R and 111 the latter agaln the lIldllCillVlGflCtflIlCQ.15 811131161 111 comparison with the non-inductive resistance than in the section R In the high volume region of controlyadjztcent the end 18 the '3 change of impedance,at a given frequency,

is relativelygreat per unit movement of the contactk and it requires no particular g-nicetyof rotatable adjustment of the knob 27 toeffect desired: change in volume. However at the region of low volume controletoward or adjacent the terminal 17, to eifect (a given percentage changein volume requires a much smallerchange in impedance and this lmpliesa smaller or nicer adjustmentiof the knob27. Toobviate thisfineness or nicety 0f adjustment,"the-impedance change per unit ofmovement ofthe contact K is much less due to the increased spacing of the re- 'sistance-turns. 'wBy :utilizinga plurality of sections having diflerent aimpedance characteristics asmooth and gently changing volumecontrolis possible and particularly in the section iR the impedance variation may be said to be acocmplished predominatingly by change of vresistance rather than by change of inductance; and todesser extent the sameis true of section R In Fig. 8 there is graphically illustrated the general nature of the volume control effected at 400 meters, for example. Ordinates'are magnitudes of impedances, and ab scissae are dial positions or positions of the contact K or knob 27 in degrees departure from end 17 of the resistance unit.

For the range covered by the resistance section R the impedance change is shown to be small and occupying as much as about 40 degrees of movement of the contact K. In the section It the impedance change is reater per unit movement of the contact K an again about 40 degrees of movement of the contact are required to traverse this section. In the section R the impedance change per unit of movement of the contact is still greater and to traverse that section the contact moves about 220 degrees. The changes in volume for the different positions of the contact K are in a general way similar to the impedance changes.

For other frequencies within the range of tuning of the set the characteristics will generally be similar to that of Fig. 8. For wave lengths shorter than 400 meters the characteristics will rise more rapidly, and for wave lengths greater than 400 meters the characteristics will rise less rapidly.

While a resistance unit R which is noninductive is suitable for volume control, and is preferable, nevertheless from practical considerations it is preferred to construct the unit by winding its conductor upon a form, with the result that there inheres in the unit some inductance. With such inductance present however the magnitude of its change per unit of movement of the control contact K is, as described, made small in the region of low volume control, whereby both the resistance and inductance changes per unit of movement of the control contact K in the region of low volume control are smaller than in the region of high volume control.

t will be understood that my invention is not limited to the use of control resistance with mechanical coupling of the rotors of the tuning condenser, since those rotors may be independently operable if desired.

l/Vhile the circuit arrangement herein disclosed is shown as one stabilized by use of the resistances R and R in association with reversed poling of the radio frequency coupling transformers it will be understood that other systems of stabilization or of neutralization may be utilized.

A control resistance R of the character herein described may be utilized in other 0- sitions than that indicated in Fig. 1. Sue a resistance may be connected in shunt with the primary of one or more of the coupling transformers T, T and T and when two or more are utilized the control contacts may be mechanically coupled for adjustment in unison, and they may be staggered so that circuit is closed through them dissimultaneousl at their ends 18 as disclosed in my copen ing application serial No. 245,851, filed J anuary 11, 1928.

For brevity the term resistance as employed in the ap ended claims shall be understood to compre end both non-inductive and inductive resistances.

What I claim is:

L'A radio receiving system comprising the combination with an absorption structure, of a receiving set comprising a plurality of thermionic devices in cascade, and a signal-reproducing instrument, the input electrodes of the first of said cascaded devices operatively related to said absorption structure, and means for controlling the magnitude of response of said instrument comprising a wound resistor and a coo crating control contact disposed in a path e ectively in shunt to said input electrodes, the resistance change per turn being uniform and the inductance change er turn being of different magnitudes where y equal increments of movement of said control contact along said resistor effect different impedance changes.

2. A radio receiving system comprising the combination with an absorption structure, of a' receiving set comprising a plurality of thermionic devices in cascade, and a signal reproducing instrument, the in ut electrodes of the first of said'cascaded evices operatively related to said absorption structure and means for controlling the magnitude 0 response of said instrument comprising a wound resistor and a cooperating control contact disposed in a path efiectively in shunt to said input electrodes, said resistor being of uniform resistance er unit length of conductor and the convo utions thereof so disposed that equal increments of movement of said control contact along said resistor effeet smaller impedance changes in a region of low than in a region of high magnitude of response of said instrument.

3. A radio receiving system comprising the combination with an absorption structure of a receiving setcomprising a plurality of thermionic devices in cascade, and a signalreproducing instrument, the in ut electrodes of the first of said cascaded evices operatively related to said absorption structure and means for controlling the magnitude 0 response of said instrument compr1sing a resistance and a,cooperatin control contact disposed in a path eflectivefy in shunt to said input electrodes, the resistance conductor disposed in turns whose spacing increases in the direction of movement of said control contact from re ion of high to region of low magnitude 0 response of said instrument.

4. A radio receiving system comprising the combination with an absorption structure, of a receiving set comprising a plurality of thermionic devices in cascade, and a signallit?" re roducing instrument, the in ut electrodes 0 the first of said cascaded evices operatively related. to said absorption structure, and means for controlling the magnitude of response ofsaid instrument comprising a resistance and a cooperatinp; control contact disposed in a path effective y in shunt to said input electrodes, said resistance comprising serially connected sections,each section comw prising equally spaced turns of the resistance conductor the spacing of turns'in a section corresponding to lower magnitude of response of said instrument being greater than in a section corresponding to igher magnitude of 15 response of said instrument.

5. A radio receivin system comprising the combination with a t ermionic device, input and output systems therefor an impedance in one of said systems, a si a '-reproducing ingo strument operatively re a-ted to said output system, and meansfor controlling the magnitude of response of said instrument 'comprisin a wound resistor and acooperating contro contactdisiposed in a path eii'ective s5 1y in shunt to sai impedance, said resistor being of uniform resistance per turn and the turns so disposed that equal increments of movement 0 said control contact along said resistor efiect smaller impedance changes in so a region of low than in a region of high magnitude of res ons'e of said instrument.

' THUR ATWATER KENT. 

